/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.wicket.proxy;
import java.io.ObjectStreamException;
import java.io.Serializable;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.Arrays;
import java.util.List;
import net.sf.cglib.core.DefaultNamingPolicy;
import net.sf.cglib.core.Predicate;
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
import org.apache.wicket.util.io.IClusterable;
import org.apache.wicket.WicketRuntimeException;
import org.apache.wicket.model.IModel;
import org.apache.wicket.core.util.lang.WicketObjects;
/**
* A factory class that creates lazy init proxies given a type and a {@link IProxyTargetLocator}
* used to retrieve the object the proxy will represent.
* <p>
* A lazy init proxy waits until the first method invocation before it uses the
* {@link IProxyTargetLocator} to retrieve the object to which the method invocation will be
* forwarded.
* <p>
* This factory creates two kinds of proxies: A standard dynamic proxy when the specified type is an
* interface, and a CGLib proxy when the specified type is a concrete class.
* <p>
* The general use case for such a proxy is to represent a dependency that should not be serialized
* with a wicket page or {@link IModel}. The solution is to serialize the proxy and the
* {@link IProxyTargetLocator} instead of the dependency, and be able to look up the target object
* again when the proxy is deserialized and accessed. A good strategy for achieving this is to have
* a static lookup in the {@link IProxyTargetLocator}, this keeps its size small and makes it safe
* to serialize.
* <p>
* Example:
*
* <pre>
* class UserServiceLocator implements IProxyTargetLocator
* {
* public static final IProxyTargetLocator INSTANCE = new UserServiceLocator();
*
* Object locateProxyObject()
* {
* MyApplication app = (MyApplication)Application.get();
* return app.getUserService();
* }
* }
*
* class UserDetachableModel extends LoadableDetachableModel
* {
* private UserService svc;
*
* private long userId;
*
* public UserDetachableModel(long userId, UserService svc)
* {
* this.userId = userId;
* this.svc = svc;
* }
*
* public Object load()
* {
* return svc.loadUser(userId);
* }
* }
*
* UserService service = LazyInitProxyFactory.createProxy(UserService.class,
* UserServiceLocator.INSTANCE);
*
* UserDetachableModel model = new UserDetachableModel(10, service);
*
* </pre>
*
* The detachable model in the example above follows to good citizen pattern and is easy to unit
* test. These are the advantages gained through the use of the lazy init proxies.
*
* @author Igor Vaynberg (ivaynberg)
*
*/
public class LazyInitProxyFactory
{
/**
* Primitive java types and their object wrappers
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
private static final List PRIMITIVES = Arrays.asList(String.class, byte.class, Byte.class,
short.class, Short.class, int.class, Integer.class, long.class, Long.class, float.class,
Float.class, double.class, Double.class, char.class, Character.class, boolean.class,
Boolean.class);
/**
* Create a lazy init proxy for the specified type. The target object will be located using the
* provided locator upon first method invocation.
*
* @param type
* type that proxy will represent
*
* @param locator
* object locator that will locate the object the proxy represents
*
* @return lazily initializable proxy
*/
public static Object createProxy(final Class<?> type, final IProxyTargetLocator locator)
{
if (PRIMITIVES.contains(type) || Enum.class.isAssignableFrom(type))
{
// We special-case primitives as sometimes people use these as
// SpringBeans (WICKET-603, WICKET-906). Go figure.
return locator.locateProxyTarget();
}
else if (type.isInterface())
{
JdkHandler handler = new JdkHandler(type, locator);
try
{
return Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(),
new Class[] { type, Serializable.class, ILazyInitProxy.class,
IWriteReplace.class }, handler);
}
catch (IllegalArgumentException e)
{
/*
* STW: In some clustering environments it appears the context classloader fails to
* load the proxied interface (currently seen in BEA WLS 9.x clusters). If this
* happens, we can try and fall back to the classloader (current) that actually
* loaded this class.
*/
return Proxy.newProxyInstance(LazyInitProxyFactory.class.getClassLoader(),
new Class[] { type, Serializable.class, ILazyInitProxy.class,
IWriteReplace.class }, handler);
}
}
else
{
CGLibInterceptor handler = new CGLibInterceptor(type, locator);
Enhancer e = new Enhancer();
e.setInterfaces(new Class[] { Serializable.class, ILazyInitProxy.class,
IWriteReplace.class });
e.setSuperclass(type);
e.setCallback(handler);
e.setNamingPolicy(new DefaultNamingPolicy()
{
@Override
public String getClassName(final String prefix, final String source,
final Object key, final Predicate names)
{
return super.getClassName("WICKET_" + prefix, source, key, names);
}
});
return e.create();
}
}
/**
* This interface is used to make the proxy forward writeReplace() call to the handler instead
* of invoking it on itself. This allows us to serialize the replacement object instead of the
* proxy itself in case the proxy subclass is deserialized on a VM that does not have it
* created.
*
* @see ProxyReplacement
*
* @author Igor Vaynberg (ivaynberg)
*
*/
protected static interface IWriteReplace
{
/**
* write replace method as defined by Serializable
*
* @return object that will replace this object in serialized state
* @throws ObjectStreamException
*/
Object writeReplace() throws ObjectStreamException;
}
/**
* Object that replaces the proxy when it is serialized. Upon deserialization this object will
* create a new proxy with the same locator.
*
* @author Igor Vaynberg (ivaynberg)
*
*/
static class ProxyReplacement implements IClusterable
{
private static final long serialVersionUID = 1L;
private final IProxyTargetLocator locator;
private final String type;
/**
* Constructor
*
* @param type
* @param locator
*/
public ProxyReplacement(final String type, final IProxyTargetLocator locator)
{
this.type = type;
this.locator = locator;
}
private Object readResolve() throws ObjectStreamException
{
Class<?> clazz = WicketObjects.resolveClass(type);
if (clazz == null)
{
ClassNotFoundException cause = new ClassNotFoundException(
"Could not resolve type [" + type +
"] with the currently configured org.apache.wicket.application.IClassResolver");
throw new WicketRuntimeException(cause);
}
return LazyInitProxyFactory.createProxy(clazz, locator);
}
}
/**
* Method interceptor for proxies representing concrete object not backed by an interface. These
* proxies are representing by cglib proxies.
*
* @author Igor Vaynberg (ivaynberg)
*
*/
private static class CGLibInterceptor
implements
MethodInterceptor,
ILazyInitProxy,
Serializable,
IWriteReplace
{
private static final long serialVersionUID = 1L;
private final IProxyTargetLocator locator;
private final String typeName;
private transient Object target;
/**
* Constructor
*
* @param type
* class of the object this proxy was created for
*
* @param locator
* object locator used to locate the object this proxy represents
*/
public CGLibInterceptor(final Class<?> type, final IProxyTargetLocator locator)
{
super();
typeName = type.getName();
this.locator = locator;
}
/**
* @see net.sf.cglib.proxy.MethodInterceptor#intercept(java.lang.Object,
* java.lang.reflect.Method, java.lang.Object[], net.sf.cglib.proxy.MethodProxy)
*/
public Object intercept(final Object object, final Method method, final Object[] args,
final MethodProxy proxy) throws Throwable
{
if (isFinalizeMethod(method))
{
// swallow finalize call
return null;
}
else if (isEqualsMethod(method))
{
return (equals(args[0])) ? Boolean.TRUE : Boolean.FALSE;
}
else if (isHashCodeMethod(method))
{
return hashCode();
}
else if (isToStringMethod(method))
{
return toString();
}
else if (isWriteReplaceMethod(method))
{
return writeReplace();
}
else if (method.getDeclaringClass().equals(ILazyInitProxy.class))
{
return getObjectLocator();
}
if (target == null)
{
target = locator.locateProxyTarget();
}
return proxy.invoke(target, args);
}
/**
* @see org.apache.wicket.proxy.ILazyInitProxy#getObjectLocator()
*/
public IProxyTargetLocator getObjectLocator()
{
return locator;
}
/**
* @see org.apache.wicket.proxy.LazyInitProxyFactory.IWriteReplace#writeReplace()
*/
public Object writeReplace() throws ObjectStreamException
{
return new ProxyReplacement(typeName, locator);
}
}
/**
* Invocation handler for proxies representing interface based object. For interface backed
* objects dynamic jdk proxies are used.
*
* @author Igor Vaynberg (ivaynberg)
*
*/
private static class JdkHandler
implements
InvocationHandler,
ILazyInitProxy,
Serializable,
IWriteReplace
{
private static final long serialVersionUID = 1L;
private final IProxyTargetLocator locator;
private final String typeName;
private transient Object target;
/**
* Constructor
*
* @param type
* class of object this handler will represent
*
* @param locator
* object locator used to locate the object this proxy represents
*/
public JdkHandler(final Class<?> type, final IProxyTargetLocator locator)
{
super();
this.locator = locator;
typeName = type.getName();
}
/**
* @see java.lang.reflect.InvocationHandler#invoke(java.lang.Object,
* java.lang.reflect.Method, java.lang.Object[])
*/
public Object invoke(final Object proxy, final Method method, final Object[] args)
throws Throwable
{
if (isFinalizeMethod(method))
{
// swallow finalize call
return null;
}
else if (isEqualsMethod(method))
{
return (equals(args[0])) ? Boolean.TRUE : Boolean.FALSE;
}
else if (isHashCodeMethod(method))
{
return hashCode();
}
else if (isToStringMethod(method))
{
return toString();
}
else if (method.getDeclaringClass().equals(ILazyInitProxy.class))
{
return getObjectLocator();
}
else if (isWriteReplaceMethod(method))
{
return writeReplace();
}
if (target == null)
{
target = locator.locateProxyTarget();
}
try
{
return method.invoke(target, args);
}
catch (InvocationTargetException e)
{
throw e.getTargetException();
}
}
/**
* @see org.apache.wicket.proxy.ILazyInitProxy#getObjectLocator()
*/
public IProxyTargetLocator getObjectLocator()
{
return locator;
}
/**
* @see org.apache.wicket.proxy.LazyInitProxyFactory.IWriteReplace#writeReplace()
*/
public Object writeReplace() throws ObjectStreamException
{
return new ProxyReplacement(typeName, locator);
}
}
/**
* Checks if the method is derived from Object.equals()
*
* @param method
* method being tested
* @return true if the method is derived from Object.equals(), false otherwise
*/
public static boolean isEqualsMethod(final Method method)
{
return (method.getReturnType() == boolean.class) &&
(method.getParameterTypes().length == 1) &&
(method.getParameterTypes()[0] == Object.class) && method.getName().equals("equals");
}
/**
* Checks if the method is derived from Object.hashCode()
*
* @param method
* method being tested
* @return true if the method is defined from Object.hashCode(), false otherwise
*/
public static boolean isHashCodeMethod(final Method method)
{
return (method.getReturnType() == int.class) && (method.getParameterTypes().length == 0) &&
method.getName().equals("hashCode");
}
/**
* Checks if the method is derived from Object.toString()
*
* @param method
* method being tested
* @return true if the method is defined from Object.toString(), false otherwise
*/
public static boolean isToStringMethod(final Method method)
{
return (method.getReturnType() == String.class) &&
(method.getParameterTypes().length == 0) && method.getName().equals("toString");
}
/**
* Checks if the method is derived from Object.finalize()
*
* @param method
* method being tested
* @return true if the method is defined from Object.finalize(), false otherwise
*/
public static boolean isFinalizeMethod(final Method method)
{
return (method.getReturnType() == void.class) && (method.getParameterTypes().length == 0) &&
method.getName().equals("finalize");
}
/**
* Checks if the method is the writeReplace method
*
* @param method
* method being tested
* @return true if the method is the writeReplace method, false otherwise
*/
public static boolean isWriteReplaceMethod(final Method method)
{
return (method.getReturnType() == Object.class) &&
(method.getParameterTypes().length == 0) && method.getName().equals("writeReplace");
}
}